The present invention relates to a sheet metal punching machine.
Currently known sheet metal punching machines comprise a frame; a work table supported on the frame; and a punching unit located over the work table at a work station. The punching unit comprises a counterpunch holder unit located beneath the work table at the work station; a ram located over the work table at the work station; and a punch holder unit located over the work table, between the ram and the counterpunch holder unit.
The counterpunch holder unit comprises a supporting disk, which is located beneath and parallel to the work table and supports a number of counterpunch holder assemblies, each fitted integrally with at least a respective counterpunch. The supporting disk is rotated in steps about an axis of rotation perpendicular to the work table to position a respective counterpunch at the work station.
Similarly, the punch holder unit comprises a respective supporting disk, which is located over and parallel to the work table and supports a number of punch holder assemblies, each fitted integrally with at least a respective punch. The supporting disk is rotated in steps about an axis of rotation perpendicular to the work table to position a respective punch at the work station.
At the work station, the ram, punch and counterpunch are aligned along a common axis perpendicular to the work table; and known machines also comprise a sheet handling device for positioning a sheet between the punch and the counterpunch at the work station.
In the course of a normal operating cycle, machines of the above type require replacement of some of the punches and/or counterpunches, which must be done with the machine at rest. For which purpose, machines of the above type may feature a manipulating assembly to facilitate removal and replacement of the punches and/or counterpunches.
The main drawback of such machines is the amount of work and downtime involved in replacing the counterpunches, which may weigh heavily on the running cost of the machine.
While reducing downtime, which nevertheless is still considerable, currently known manipulating assemblies seriously complicate the structure of the machine, thus frequently impairing reliability and greatly increasing production cost. Such assemblies in fact are extremely complicated and expensive, and are subject to breakdowns which in themselves prevent the machine from being operated.